A radiation generating tube, which is used as a radiation source, generates radiation by emitting electrons from an electron source within the radiation generating tube (radiation emitting source) in which a vacuum is maintained, and making the electrons collide with the target, which is formed from a metal material such as tungsten having a large atomic number.
Incidentally, in order to efficiently generate electrons from an electron source and to extend the life of the radiation generating tube, it is necessary to keep the inside of the radiation generating tube at a vacuum for a long period of time. Japanese Patent Application Laid-Open No. 2000-306533 discloses a technique for keeping the inside of the radiation generating tube at a vacuum by brazing the perimeter of the target to a target holding ring of the radiation generating tube (X-ray tube), in a radiation generating tube that uses a transmitting type target.
In addition, in the radiation generating tube, the radiation generated in the target is emitted in all directions, and accordingly, it is general to shield the unwanted radiation, that is, radiation other than that required for photography, by providing a radiation shielding member. Japanese Patent Application Laid-Open No. 2007- 265981 discloses a structure in which the radiation shielding member is arranged at the electron incident side and the radiation extraction side of the transmitting type target.